Rick Santorum found himself in unfamiliar territory on Wednesday night: at the center of attention in a Republican primary debate. The CNN forum in Arizona was the first in almost a month, and the only debate held since upsets in Minnesota and Colorado put Santorum in the top-tier of contention with Mitt Romney. And while the former Senator has shown competence on the dais, the new level of scrutiny threw him off-balance.

A threatened Romney was not a cowed Romney; he was on Santorum from the outset: “Voting for the debt ceiling five different times without voting for compensating cuts,” he said of Santorum’s congressional record. “Voting to fund Planned Parenthood, voting to expand the Department of Education. During his term in the Senate spending grew by some 80% of the federal government.”

Santorum went into a defensive crouch, adroit with his counterpoints at first. He ripped Romney on taxes and spoke about his own record at length. But Romney’s attacks were quick and pithy. And Santorum’s parries lagged as the night wore on. When the conversation switched to earmarks and Santorum criticized him for seeking government assistance for the Salt Lake City Olympic Games, Romney said, “When I was fighting to save the Olympics, you were fighting to save the ‘Bridge to Nowhere,'” in reference to the $400 million exemplar of congressional graft. Santorum delivered a apologia on congressional earmarking.

When Romney defended his opposition to the 2009 auto industry rescue, Santorum accused him of hypocrisy in opposing a bailout for Detroit after supporting one for Wall Street. “Nice try, but now let’s look at the facts,” Romney said before firing off a few lines on Santorum’s votes in support of airlines and the steel industry. Santorum again defended his record at length.

Even in debating the health care reforms he enacted in Massachusetts, which are similar to the tenets of President Obama’s national overhaul, Romney managed to turn the conversation to Santorum’s past. First, he noted that Santorum endorsed him in 2008, long after CommonwealthCare was on the books. Then he made the audacious argument that it was Santorum’s 2004 endorsement of Arlen Specter, who later switched parties and voted with Obama, that led to the federal legislation’s passage. “He voted for ObamaCare. If you had not supported him, if we had said no to Arlen Specter, we would not have ObamaCare,” Romney said. “So don’t look at me, take a look in the mirror.”

And then there were the unforced errors. When asked by an audience member about his stance on No Child Left Behind, George W. Bush’s education law, Santorum volunteered that his vote for it was pure political expediency. “It was against the principles I believed in,” he said. “But, you know, when you’re part of the team, sometimes you take one for the team.” A different point about contraception—Santorum is personally opposed to the practice, but would not seek to ban it—came out sounding similarly squishy. “I have a personal moral objection” to contraception, he said, “but I’ve voted for bills that included it too.”

Santorum was by no means feckless in Wednesday’s debate. He actually had one of the better lines of the night, poking holes in Romney’s frequent boast that he balanced the budget every year as governor of Massachusetts: “Don’t go around bragging about something you have to do,” he said in reference to the state’s constitutional requirement of a balanced budget. “Michael Dukakis balanced the budget for 10 years. Does that make him qualified to be president of the United States? I don’t think so.” But he was still clearly adjusting to his new place at center stage of the Republican primary. With the last debate before crucial contests next Tuesday in Michigan and Arizona—possibly the final debate of the primary season—now over, Santorum may lack the venue to give voters another impression.